1. Field of the Invention
The present invention relates to an ink-jet printhead and a manufacturing method thereof, and more particularly, to a method of forming an anti-wetting layer on a nozzle plate and processing a nozzle when an ink-jet printhead is manufactured.
2. Description of the Related Art
Ink ejection mechanisms for ink-jet printers include an electro-thermal transducer ejecting ink by generating bubbles in ink using a heat source in a bubble-jet method, and an electro-mechanical transducer ejecting ink using volume variations of ink caused by the deformation of a piezoelectric device.
The bubble-jet method using the electro-thermal transducer is further divided into a top-shooting method, a side-shooting method, and a back-shooting method according to a growing direction of the bubbles and an ejecting direction of ink droplets. The top-shooting method is a method in which the growing direction of the bubbles is the same as the ejecting direction of the ink droplets, the side-shooting method is a method in which the growing direction of the bubbles is perpendicular to the ejecting direction of the ink droplets, and the back-shooting method is a method in which the growing direction of the bubbles is opposite to the ejecting direction of the ink droplets.
An ink-jet printhead supporting these ink ejection mechanisms includes a nozzle plate having a nozzle (orifice) through which the ink droplets are ejected. The nozzle plate directly faces paper to be printed on and presents various factors which may affect ejection of the ink droplets ejected through the nozzle. Among these factors, there is a hydrophobic property of a surface of the nozzle plate. When the hydrophobic property is limited, that is, when the nozzle plate has a hydrophile property, a portion of ink ejected through the nozzle is soaked into the surface of the nozzle plate and contaminates the surface of the nozzle plate, and a size, a direction, and a speed of the ejected ink droplets are nonuniform. In order to solve these problems, a coating layer for anti-wetting is formed on the surface of the nozzle plate.
FIGS. 1A and 1B are schematic cross-sectional views of a conventional ink-jet printhead 10 supporting a back-shooting method in which a surface of a multilayer nozzle plate 12 is anti-wetted. Referring to FIG. 1A, a hemispheric chamber 14 is formed at a center of a top surface of a substrate 11. A trapezoidal channel-shaped manifold 17 is formed under the chamber 14, and the chamber 14 and the manifold 17 are connected to each other through a passage 16. The multilayer nozzle plate 12 is formed on the top surface of the substrate 11. The nozzle plate 12 is a membrane that is formed by stacks formed on the substrate 10, and includes a nozzle (or orifice) 18, that is disposed at a center of the chamber 14 and a bubble guide 18a that is extended into an inside of the chamber 14 and is formed around the nozzle 18.
The nozzle plate 12 includes a lower insulating layer 12a, an intermediate insulating layer 12b, and an upper insulating layer 12c. A heater 13 surrounds the nozzle 18, is formed between the lower insulating layer 12a and the intermediate insulating layer 12b, and is connected to a pad 22. An interconnection layer 15 is connected to the heater 13 and is formed between the intermediate insulating layer 12b and the upper insulating layer 12c. In the above structure, the upper insulating layer 12c is formed of a single layer or multilayer stack. A hydrophobic coating layer 19 is formed on the upper insulating layer 12c. Preferably, the hydrophobic coating layer 19 is formed at least on the surface of the nozzle plate 12 around the nozzle 18. Here, metal, such as gold-plated nickel (Ni), gold (Au), palladium (Pd), or tantalum (Ta), and a perfluoronated alkane and silane compound with a high hydrophobic property, such as Fluorinated Carbon (FC), F-Silane, or Diamond Like Carbon (DLC), are used for the hydrophobic coating layer 19.
The hydrophobic coating layer 19 may be formed by a wetting method, such as a spray coating method or spin coating, and the hydrophobic coating layer 19 is deposited using a drying method, such as plasma enhanced-chemical vapor deposition (PE-CVD) and sputtering. The hydrophobic coating layer 19 is formed after the nozzle 18 and the chamber 14 have been already formed. In this case, when a hydrophobic material is inserted into the chamber 14 through the nozzle 18, a hydrophobic material layer 19′ is formed on an entire surface or a part of a bottom surface of the chamber 14. In a worse case, the hydrophobic material layer 19′ may be formed on an inner wall of the passage 16 connected to the manifold 17. When the hydrophobic material layer 19′ is formed inside the chamber 14 and the passage 16, ink is not smoothly supplied to the chamber 14 due to the hydrophobic property of the hydrophobic material, or ink may not be supplied at all to the chamber. Thus, after the hydrophobic material is formed on the surface of the nozzle plate 12, the hydrophobic material layer 19′ formed in the chamber 14 and the passage 16 is removed by a subsequent O2 plasma etching process. However, when the hydrophobic material in the chamber 14 is removed using O2 plasma, the nozzle plate 12, in particular, the hydrophobic coating layer 18 formed on the surface of the nozzle plate 12 may be excessively exposed to O2 plasma, and thus may be severely damaged.
As shown in FIG. 1A, the nozzle 18 has a funnel shape in which an entire shape of the nozzle 18 is enlarged gradually from an end of the bubble guide 18a and finally opened widely to an outside of the nozzle, thereby forming an ink ejection portion having an enlarged and opened structure. The enlarged and opened structure is formed by a structural profile of a lower stack including the heater 13 and an interconnection layer 15.
The enlarged and opened structure is a portion in which ink 14a guided through the bubble guide 18a splits into droplets and ejected. When the droplets are ejected from the enlarged and opened ink ejection portion of the nozzle 18, pressure has been already lowered before the droplets are completely separated from the nozzle 18, and thus it is difficult to form the droplets having a preferable shape and a high speed. Since the droplets pass through the enlarged and opened portion when the progressing direction of the droplets is not guided while a sufficient progressing distance is maintained, the ejected droplets cannot travel straight in a stable manner.
FIG. 1B is a scanning electronic microscope (SEM) photo schematically illustrating a sectional structure of the conventional ink-jet printhead having the shape of the nozzle 18 in which an opened end is enlarged gradually and opened widely in a form of a funnel.
As shown in FIG. 1B, since the nozzle 18 is enlarged and opened via the bubble guide 18a, problems, such as a deteriorating straight-traveling property of the droplets, an occurrence of the droplets having no preferable shape, and a slow ejection speed of the droplets due to a hydrodynamic result caused by the shape of the nozzle, may occur. In order to solve the problems caused by the enlarged and opened nozzle 18, it is needed that the bubble guide and the enlarged and opened portion that are extended into the bubble guide, have predetermined consecutive diameters, or that the opening of the nozzle that extends into the bubble guide, has a cone shape and its diameter reduces gradually in the progressing direction of the droplets.